Some rifles include stocks which have a generally upright interior surface which forward of the butt surface. Such rifles also have a longitudinal countersunk bore communicating between the upright interior surface and the butt surface for carrying a bolt for attaching accessories which are often mounted to the interior surface. Marksmen using rifles either as military snipers or as target shooters will often support the forward end of a rifle with a stationary bi-pod support and simultaneously support the butt end of the rifle in a way that provides fine adjustment of the elevation of the rifle. Accordingly, it is advantageous if an adjustable support is provided for rifles having an interior mounting surface as described above. Applicant's U.S. Pat. No. 5,248,868, which is incorporated here as if repeated verbatim hereafter, teaches an adjustable support for supporting the stock end of a rifle. The adjustable support taught in U.S. Pat. No. 5,248,868 is generally adapted for clamping to the type of firearm stock having sling stud imbedded in the lower surface of the firearm stock toward the butt end of the stock. It is also advantageous if an adjustable support can be rotated into a retracted position with a minimum of effort and conversely rotated into an extended position for use with a minimum of effort.